An integrated study of oogenesis and early development holds great promise for providing a clear understanding of the events of cleavage and early determination in embryos. From these studies on Drosophila embryos we will provide a basis for the examination of specific components of the egg which have developmental importance. Two approaches will be used. In the first, we will analyze components of the germ plasm and test their in vivo activity. Monoclonal antibodies will be prepared to the protein components and the RNA will be copied, cloned, and analyzed. In situ hybridization of cloned DNA will be made to sections of eggs to verify the origin of the RNA and to study its formation. In situ hybridization to the polytenic chromosomes will localize the site of synthesis of the RNA so that mutants can be obtained affecting this function. Antibodies to the proteins will be useful in studying the synthesis of the polar granule, its fate during development, and its genomic origen. The second approach will be to study in detail the pole cells which are the first cells to become determined in the embryo. In vitro cultures will be developed, which will enable biochemical and molecular studies of their metabolism. The stability of their phenotype will be tested, RNA and protein synthetic patterns will be compared to other embryonic cells, and the specific surface antigens will be identified and analyzed. Thus, from these analyses we will gain a detailed knowledge of the processes involved in the formation and localization of the functional germ plasm during early development, and finally the molecular characteristics of pole cells after their determination. This knowledge should provide the basis for a specific theory of how early embryonic determination is produced and form the basis for a model of determination.